1. Field of the Invention
The present invention concerns a highly weather-resistant, single package, crosslinkable emulsion of excellent water proofness, weather-resistance and initial drying property. More particular, it provides a highly weather-resistant, single package, crosslinkable emulsion capable of forming a coating layer which rapidly dries to cure at the initial stage of coating, exhibits long lasting excellent water proofness and weather-resistance, and further, having satisfactory gloss retainability, shape retainability, chemical resistance, solvent resistance and so on.
2. Description of the Related Art
Emulsion type paint compositions have hitherto been produced by emulsion polymerization using various kinds of emulsifiers and have generally been used in the field of paints taking advantages of resulting in non-public pollution, good operability and of saving resources. However, since hydrophilic emulsifiers used for emulsion polymerization remain in the coating layer even after water is evaporated to form a coating film and tend to be localized at the boundary between each of original particles, this gives an undesired effect on various properties of the coating layer such as water proofness.
As a method of improving drawbacks in the emulsion type paint composition due to emulsifiers as described above, there have been proposed, for example, a soap free method of using a great amount of potassium persulfate or the like, a method of using a high molecular emulsifier and a method of using a reactive emulsifier having a polymerizable unsaturated group in the molecular structure but the water proofness is still insufficient. In view of the above, Japanese Patent Laid Open Sho 63-258913 (1988) discloses an invention for obtaining an aqueous resin dispersion of excellent water proofness by using an emulsifier containing an unsaturated carboxylic acid as the essential monomer ingredient and polymerized under the presence of a polymerization regulator, and polymerizing the polymerizable monomer ingredients containing the polymerizable monomer capable of reacting with carboxylic groups. According to this method, crosslinking reaction between the emulsifier and the aqueous resin proceeds upon evaporating water to form a coating film and the emulsifier is bonded and incorporated in the crosslinking structure, so that molecules of the emulsifier having the surface activity do not remain in the coating film and water proofness can be improved sufficiently. However, there still remains a problem for the initial drying property and long lasting weather-resistance is also insufficient.
In the paint composition, the weather-resistance is also an important physical property. In view of the water proofness, since acrylic or methacrylic [hereinafter collectively referred to as (meth)acrylic] resin is excellent compared with a vinyl ester resin or alkyd resin, the former has been generally used in the field of paints. However, the gloss retainability in an accelerated weather-resistance (a test using a Sunshine Weather-o-meter) is approximately 1000 hours at the most. Therefore, to improve the weather-resistance, it has been attempted to add a UV-absorber or to copolymerize a UV-absorbing monomer, but the long lasting stability is insufficient and yellowing or the like because of the UV-absorbing ingredient caused, although the weather-resistance can be improved to some extent.
Besides the (meth)acrylic resin, silicone and fluoro resins are listed as the resins which have excellent long lasting weather-resistance. However, they are poor in aesthetic feeling such as in gloss or shape retainability, or operability represented by pigment dispersibility, as well as the cost is expensive, so that their application has been restricted at present.
Accordingly, an object of the present invention is to improve the foregoing problems of the paint composition in the prior art. And it is an object thereof to provide a highly weather-resistant, single package, crosslinkable emulsion capable of forming a coating layer of excellent initial drying property and also having excellent physical properties such as water proofness, gloss, shape retainability and long lasting weather-resistance.